一個小小的傳奇 ----A Little Legend
BBC LS3/5A
原載於HiFi News & Record Review，1990年3月號
作者： Trevor Butler
翻譯： 阿蜜
排版：abrams
很難找到任何一個方盒子，如同BBC LS3/5A一般，能勾起如此多的情緒反應，或是製造出這麼多的迷思與誤解。光是它的名字，就引起了困惑，而實際上它只是單純的遵循了BBC的器材編碼方式。依循此一方式，音箱cabinets最前面的兩個字母以CT代表，分音器filters為FL，而喇叭loudspeakers則為LS。編碼中的3表示此一設計主要是供外製轉播(outside broadcast-OB)所用。如果此一編碼為5，則代表供錄音室廣播用，如LS5/9即是。在斜線後的5則是型號。LS3/5即取代較早的OB喇叭如LS3/1。所以我們可以理解LS3/5是當初開始製造時的編號。編號最後的A則是後來加上去的，用以表明第一次也是唯一一次的設計修正。如果有後續的修改的話，則會以B來標示，但那從未發生，也不太像會發生，其原因後文將述明。
There can hardly be another single box which as provoked as much emotive comment，or given rise to so many myths and misunderstandings，as the BBC LS3/5A。The very name has caused confusion，but in fact it simply follows the BBC's coded equipment format。In this，cabinets have the prefix 'CT'，filters 'FL'，and loudspeakers 'LS'，hence the first two letters。The figure '3' in the code indicates that the design is primarily for outside broadcast (OB) use。A figure '5' would mean studio broadcasting，as LS5/9。The number '5' after the stroke is the model number，the LS3/5 supplanting previous
OB speakers like the LS3/1。So we arrive at LS3/5 which was the title of the initial model。Later the 'A' was added to indicate the first and only design alteration to the original specification。Any further specification change would result in a 'B'; but that hasn't happened，and isn't likely to，for reasons which will become apparent。
此一喇叭的設計概念，是為因應BBC的某些製作環境：當以耳機監聽並不能令人滿意，而又沒有足夠空間來使用Grade I監聽喇叭時。Grade I監聽喇叭是用來調整廣播節目較具決定性的音調平衡，或麥克風的擺位等。現役的Grade I監聽喇叭是LS5/8與LS5/9。Grade II 監聽器則可用以監聽節目的品質，但音調平衡或麥克風擺位等則一般屬於Grade I喇叭的工作範圍，除非別無選擇。設計者因此體認到：前述情況將需要一種小型的Grade II喇叭，而為達成體積小巧的目的，犧牲部分低頻響應與響度便無可厚非。此種喇叭較可能的使用者為：電視外製轉播車的主控區，這些製作者需要以較正式混音時低的音量做監聽。
The concept of this speaker was to suit those BBC environments where monitoring on headphones was not satisfactory and yet there wasn't sufficient room for a 'Grade I' monitor。A Grade I monitor can be used for critical tonal balancing of programme material，setting of microphone positioning，etc。Current Grade I monitors are the LS5/8 and LS5/9。A grade II monitor may be used for checking the quality of programme，but balance and mic positioning are normally Grade I-checked unless there is no alternative。It was recognized that what would be required was a small Grade II unit with some sacrifice of bass response and loudness reproduction，this being justified for the sake of achieving compactness。The likely users were，for instance，the production control areas of television OB control vans，where there producer needs to listen at a lower level than that used for the actual mixing。
當時市面上並沒有現成合適的商業產品，因此BBC設在Kingswood Warren的研究部門就被要求設計一對這樣的喇叭。才不到一個星期，原型機就被做出來，並進行實地測試與評估。之所以能這麼快，是因為LS3/5的設計，是脫胎於一對實驗性喇叭，該喇叭已經在Kingswood被用來做一些音頻比例測試(acoustic scaling test)的初步工作。
There was no suitably available commercial unit，and so the Research Department of the BBC was asked to design one，at its headquarters in Kingswood Warren。Less than a week elapsed between this request and the first prototype being offered for field trials and evaluation。This came about because the LS3/5 was based around an experimental loudspeaker which had been developed for some preliminary work on acoustic scaling tests at Kingswood。
當時是以1/8比例的模型，並在1/8的波長(也就是8倍高的頻率)下錄音，某些音響技術的優缺點就可以被評估出來，而不必花大錢建構1：1的環境。當然，正因為如此，這也暗示了整個模型的再生過程所使用的器材，從放音機，喇叭，麥克風到錄音機，都要能在極高的水準下運作，其所處理的頻寬為400Hz到100kHz，以便能正確模仿一般頻寬的40Hz到15kHz。
By using one-eighth scale models，and one-eighth wavelengths (IE，8-times frequencies)，recordings can be made by which the merits of particular acoustic techniques can be assessed without the expense of a life-size environment。
Naturally，though，this implies that the entire model reproduction chain，of tape player，loudspeaker，microphone and recorder，must be capable of operating at very high quality with a frequency range of 400Hz to 100kHz，in order to be able to model accurately a typical bandwidth of，say，40Hz to 15kHz。
（该处未贴的照片，是否是本贴82＃红山老猫提供的PDF＃5中那只外星人喇叭？有谁能找到1990年3月號的HiFi News & Record Review中的这篇文章所提及的照片，帮忙翻拍上传。先表示感谢。）
照片中就是BBC在1972至1980年間所使用的的這種模型喇叭，它代表了模製過程(modeling process)的一大進步。雖然它在音質及最大輸入功率方面有其侷限，這種小喇叭的組件卻被認為具有足夠高的水準，能滿足戶外廣播所要求的特殊小型監聽器。因此，這種組合就被稱為LS3/5，並顯示出當初的模型實驗者其實已經獲致很好的成果。
Pictured is the model speaker the BBC used from 1972 until 1980，which represented a major step in the modeling process。Although it had its limitations，primarily in terms of its tonal quality and maximum power handling，components of this small loudspeaker were found to be of a sufficiently high quality to help fulfil the demand for the unusually compact monitor needed in outside broadcast use。This was therefore packaged and called the LS3/5 and showed the model experimenters to have achieved good results。
BBC自行製作了一小批這種喇叭，使用在電視轉播車的控制室中，並提供了令人滿意的效果。而後BBC終於面臨一種狀況：需要邀請外面的廠家在認證許可下製造LS3/5。實際上，Rogers在1974年2月19日發出了一則新聞稿，驕傲的宣稱將在該年4月的SONEX ’74大展中展示這種新喇叭。他們附上了一張照片與一組臨時的規格：25瓦的輸入功率，頻率響應80-20，000Hz +/-3db，或是60-20，000Hz +/-4db。分頻點設在3k Hz，低音單體為110m Plastiflex doped Bextrene 音盆，高音單體為27mm半球型Mylar振膜。定價為一只52英鎊外加營業稅!
A small number of these units where made in house by the BBC and used in television mobile-control-rooms where they gave satisfactory service。The BBC got to the stage of inviting applications to make the LS3/5 under license by outside manufacturers。Indeed，Rogers issued a press release on 19th February 1974 which proudly announced that they would be exhibiting the new design at SONEX '74，an exhibition to be held that April。They offered a photograph and a provisional specification：25W power handling with +/-3dB 80-20，000Hz and +/-4dB 60-20，000kHz。Crossover frequency was quoted at 3kHz and the units were a 110mm bass driver with a Plastiflex doped Bextrene cone and a 27mm Mylar dome tweeter。The price，&52 each plus VAT!
儘管如此，當時也出現了一些早期的問題。雖然BBC對KEF生產的B110低音單體有信心，但當他們隨後需要一批供內部使用的LS3/5時，發現低音與高音單體已經歷經重大的改變，必須要重新設計才能接續生產。因此，這款喇叭就被交給當時在大波特蘭街的BBC設計部門，要求將它修改到合適。
Alas，though，there were to be early problems。Although the BBC had confidence in the KEF B110 bass unit at the time，when a subsequent batch of in-house LS3/5s was needed it was found that the low and high frequency units had undergone significant changes and a re-design of the speaker would be required before production could resume。
Accordingly，the speaker was passed on to the BBC's Designs Department，then located in Great Portland Street，with a request to modify it so that it would once again be suitable。
當時的問題來自三方面：被改變後的B110單體，以不同於前的方式刺激箱體，導致染色的產生。這染色不僅來自低音單體，也來自音箱; 高音單體則產生出明顯的’唇齒’音(lipsy)。
The trouble was in three areas; the B110 had changed，exciting the cabinet in a different way，producing a coloration both from the LF unit and the cabinet; and the HF unit had developed a pronounced 'lipsy' quality。
為了確保音箱的共振不會引起問題，兩面側板都以瀝青墊增加其阻尼，上下箱板也做相同的處理，但更鋪上兩層。此外，一種PVC邊料被加在低音單體的框架上，其作用是將低音單體與前障板隔離(de-couple)，並使接縫密封。為降低箱內空氣共振，所有的箱內壁都再鋪上聚亞胺脂發泡材料。箱體並加以密封，以防止在高音壓時空氣滲漏產生雜音—實際上甚至連螺絲孔也被做成不透氣的。箱體的問題也與軟木材巴拉那松木製的肋條有關，這些肋條連結前障板與背板，但因為不夠硬無法有效支撐，改以櫸木代替。而背板的規格也重新制定，由原本的雲杉木三夾板改為多層的樺木夾板，如此可避免雲杉木常有的空隙。修改後的音箱被稱為CT4/11A。
In an attempt to ensure that cabinet resonance would not cause problems，the side panels had each been damped with a bituminized pad，and the top and bottom panels likewise，except that two layers were required here。In addition，a PVC edging was applied to the chassis of the LF unit and to de-couple it from the front panel and seal the join。In order to damp the air modes of resonance inside，all internal surfaces were lined with polyurethane foam。The cabinet was sealed to prevent air leaks，which might produce extraneous sounds from the high pressures produced - indeed even the screw holes were made airtight。The cabinet problems were associated with the softwood parana pine fillets which connected the back panel to the front; these had an insufficient impedance and were therefore replaced with beech。The back panel was re-specified from the precious sandwich of spruce to multi-ply birch，thus obviating the voids often associated with spruce。This then became the CT4/11A。
藉著此一修正機會，高音單體的高頻唇齒音也被加以處理。當時認為這個裸露的KEF T27 SP 1032高音單體很容易在工作場所打包綑綁時受到損害，故決定加上一層保護金屬格柵，並在Celestion HF2000單體上找到一個，稍事修改後即可適用。另外T27高音單體的振膜很小，其擴散方向近乎無指向性，故其外圍以一圈固定在前障板上的厚毛氈條加以圍繞，意在防止音箱突起的邊緣干擾造成聲音不連貫(acoustic discontinuity)。而前面網的效果也在設計中被考慮進來，因此聆聽時必須要裝上面網，以避免高音域的不平順。
The opportunity was also taken to sort out the treble lisp of the tweeter。It was felt that this unit，the KEF T27 SP1032，was vulnerable because it was exposed and could easily be damaged during rigging at a venue。It was decided to incorporate a protection grille and a suitable one was found，with some modification，from a Celestion HF2000。The tweeter is surrounded by a thick felt-strip mounted on the baffle in order to prevent acoustic discontinuity presented by the edge of the cabinet setting up an interference pattern，since the T27 radiating surface is small and the radiator nearly Omni-directional。The addition of the protection grille was wholly beneficial as it raised the output at higher frequencies and help cure the lisp。The effect of the Tygan cover on the front was taken into account in the design，and the loudspeaker should always be used with the grille on，to avoid discontinuities in the upper presence region。
在做了這許多修正之後，分音器也必須要調整，因此以FL6/23取代原來的FL6/16。經過所有這些變動，LS3/5的第一個修正版於焉誕生---LS3/5A。這最後加上的’A’有其必要，因為儘管LS3/5A的聲音近似於LS3/5，其差異卻大到無法各取一只配對做立體聲聆聽。既然只有少量的LS3/5曾被製造，這一改款並未造成太大的問題，只有約20只LS3/5必須停用。
Having carried out these changes，the crossover had to be adjusted to compensate and the new type，FL6/23 replaced the original FL6/16。Sporting these alterations the first variant of the LS3/5 was born - the LS3/5A。The 'A; suffix was necessitated because although the LS3/5A sounded similar to the LS3/5，the differences were significant enough for it not to be possible to use a mixed pair for stereo listening。Since only small quantities of the LS3/5 had been built，this did not present much of a problem and only 20 units had to be considered obsolete。
對那些並不完全熟知它的人而言，此一設計至今可說仍高度維持了當初的樣子，除了這些年來一些微小的改進外。這些小改進將後續提及。
For those not fully acquainted with it，the design is still now very much as it was then，with just a few slight enhancements which came about over the years，as will be explained。
在1977年產生了一些明顯的問題，而幾乎每個夏天，製造者的不良率都會稍稍提高。80年代初期做了一個修正，當時單體懸邊的凹陷(surround-dip)似乎稍微被更動了。解決之道為將負責控制它的分頻共振器(crossover resonator)調整到一較低頻率並更改制振電阻(damping resistor)。任何一個這類的修正都由BBC發佈給當時的製造廠家並併入執照中。當時並對高音單體並聯電容(coupling capacitor)的數值做了一些修正，這是整個平衡調整的一部分。當高音單體的材質更動時，它的’Q’值也跟著變動，並在頻率響應上產生一個輕微的偏斜(tippling)。此一並聯電容影響電路的型態並決定其制振為過度或不足(under or over damped)。為調整高音域的平衡，對FL6/23上一個tapped transformer的輸出做了調整，並且改變並聯電容以維持其分頻點。
There were a few noted difficulties in 1977，and almost every Summer saw the reject rate at the manufacturers rise slightly。The early 1980s saw a change when the surround-dip was seen to have moved slightly。This was resolved when the crossover resonator controlling it was tuned to a lower frequency and the damping resistor changed。Any alteration like this is issued by the BBC to the current manufacturers and is incorporated into their license。There have been also some adjustments to the value of the tweeter coupling capacitor; these are part of the relative balance adjustment。As the material of the tweeter alters，the 'Q' changes and there is a mild 'tippling' of the response。This coupling capacitor affects the shape of the network and decides whether it is under or over damped。To adjust the treble balance，an output from a tapped transformer on the FL6/23 is adjusted，and the coupling capacitor changed to maintain the crossover frequency。
重新評估
Re-assessment
1987年的重大修改已經在專門雜誌中被廣泛報導過了，而這次的變動主要卻來自於製造廠商的要求。經過這許多年以後，授權廠商之一Rogers的Richard Ross解釋道，雖然當時製造LS3/5A使其聽起來與測量起來均符合規格是可行的，且可以被接受;但單體符合容許誤差的良率卻有變動，尤其是低音單體。因為LS3/5A的特殊設計，雖然B110單體符合KEF的規格，剛好卻有一種特點，那就是在這種喇叭設計上最關鍵的部分，此一單體的誤差卻最不穩定。在炎熱的夏天，低音單體的不良率可以從10%到85%。從授權廠商的經濟觀點而言，這是無法被接受的。
The major re-assessment of 1987 was widely reported in the specialist press; but this time the alterations had been requested primarily by the manufacturers。As one of the licensees，Richard Ross of Rogers，explained，over the years，whilst it had been possible to make an LS3/5A which sounded and measured within spec，and which was acceptable，the number of units，in particular the woofers which were within tolerance varied。Because of the particular design of the LS3/5A，the B100s，although being to KEF's standards，happened to have the point where their tolerance was most variable occurring at the most critical point in the speakers design。In hot summers the reject rate of the bass units could be anything from 10 to 85 per cent，and，for the licensees，this was not satisfactory from an economic standpoint。
在授權廠商發現難以製造品質劃一的單元的同時，BBC也有他們自己的問題。在1987年年底，成品品質似乎朝向能被接受的底限飄移。確切的說，它們被發現在1k Hz附近的八度有2db的隆起，而這正是影響聲音平衡的關鍵地帶。之前的LS3/5A在這一頻率通常也稍微隆起，但現在它隆起的程度卻開始使人不悅。必須要強調的是，它仍然可以在Grade II監聽喇叭的要求中運作，但以Grade I的標準而言，就無法被接受。
At the same time as the licensees were finding it difficult to make consistent units，the BBC was encountering their own problems。At the end of 1987 it was noticed that the units were tending to drift towards the limit of acceptability。
Specifically，they were found to be about 2dB up at a octave around 1kHz，a particularly critical area for balance。There had always been a slight lift on the LS3/5A here，but now it started to become objectionable。It should be stressed that the units were still operating within limit for a Grade II monitor，but would have been unacceptable in a Grade I。
這件事的關鍵又發生在懸邊導致的頻率凹陷上(surround-dip)，它的確切頻率隨著時間而有數百Hz的飄移。而這又與箱體共振產生牽連，到了必須採取行動的地步。非得做一些變動，使這種喇叭能被製造得可讓BBC接受，且品質劃一，符合他們所需。
The crux of the matter was again the 'surround-dip'，the precise frequency of which varies by a few hundred Hertz over time。This had become interactive with the box resonance to the extent that action was needed。A change had to be brought about so that speakers could be manufactured which the BBC would find acceptable，to provide them with a consistent loudspeaker they designed，and wanted。
BBC將這件事知會KEF，而KEF派其”特殊產品部門”(Special Products Division)來做因應。此一問題被追本溯源，發現SP1003 B110所使用的二稀橡膠Neoprene缺乏一致性，為此，一款新的B110因應LS3/5A而設計出來。這次使用一種PVC的懸邊，其材質一致性較高，且對溫度變化較穩定，但是順服度較低。因此一個種新的蛛網狀音圈(spider voice-coil)構造就被用來使這種新單體保持與舊單體一樣的靈敏度，以獲致相同的低頻表現。這就是B110 SP1228單體。分頻器設計通常是一個爭論不休的領域，這當然也發生在LS3/5A上。幾經修改，正如報導所言，但這種喇叭的主要規格與整體聲音平衡卻維持不變。
The BBC referred the matter to KEF，who set their Special Products Division to work。The problem was traced to variations in the consistency of the Neoprene used in the making of the SP1003 B110 and so a new B110 was specifically designed for the LS3/5A。This uses a PVC surround，more consistent and temperature stable than the Neoprene but less compliant。A new spider voice-coil assembly was therefore required to give the new drive the same sensitivity as the older one，in order to achieve the bass performance。This is the B110 SP1228。Crossover design is always a source of great debate and this has certainly been the case with the LS3/5A。Changes have been made，as reported，but the main specification and overall sound balance of the speaker have remained the same。
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